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django-entity-subscription 0.4.1

Django Entity Subscription uses the power of the Django-Entity
framework to make managing subscriptions easy and powerful, for you
and your users.

Overview

This django app, includes four models:

Subscription

Unsubscribe

Medium

Source

all available from within the package entity_subscription.models.

By creating objects in these models, you and the users of your
application can have fine grained control over how users are notified
and about what they are notified. The entity_subscription app is
agnostic about how users are actually notified about the subscriptions
that are set up, but is designed to be a dependency of whatever
notification system is put in place. It is assumed that the consumer
of this library already has some idea of what notifications are going
to be sent, and what delivery methods are going to be used to send the
notifications.

Once subscription information is stored in those models, the
entity_subscription app also provides some methods to make it
easier to reason about and act on the stored subscriptions.

Subscription.objects.mediums_subscribed

Subscription.objects.is_subscribed

Sources and Mediums

The entity_subscription app creates a strong boundary between the
“source” of notifications from within an application and the “medium”
used to deliver the notification to the users of the application.

Sources

From a user of your application’s perspective a “source” is a category
of notifications that they can subscribe to, or unsubscribe from. It
could be something like “New Products” or “Important Site
Changes”.

For any given source, users may want to receive notifications over
different mediums (like “Email”, “In-site”, “text-message”). By
dividing notifications into different sources, users can choose to
receive that type of notification over whatever medium they prefer.

To achieve this within an application a “source” of notifications is
an object that describes where in the app a notification came
from. Pieces of code that originate events which lead to notifications
will want to own a Source object, or at least know the name of one,
so that they can clearly communicate the source of the
notifications they are originating.

The actual source objects in the database are fairly simple, and are
created through the standard objects.create interface. They have a
unique identifier, a user friendly display name, and a longer form
description.

fromentity_subscription.modelsimportSourceSource.objects.create(name='new_products',display_name='New Products',description='Tells you whenever a new item is available in the store.')

Mediums

From a user of your application’s perspective a “medium” is a way in
which they can be notified. Your site may support a variety of
different mediums for notifying your users of different
happenings. Examples could include Email, Text Messages, a News-Feed,
or a In-site Notification center.

Users will likely want to receive notifications through some
combination of the available mediums, but only for certain categories
of notifications. They may want some notifications that they view as
somewhat important to go to their email, notifications that are very
important to go to email and text-message, and all the rest to go to
an in-site notification center. By distinguishing between mediums in a
subscription library, users can decide how each “source” of
notifications is delivered to them.

The pieces of the application that handle actually sending
notifications will want to own a Medium object that describes
them, or at least know the unique name of one. This enables the code
sending notifications to handle subscriptions appropriately.

As with sources, The actual medium objects in the database are fairly
simple, and are created through the standard objects.create
interface. They have a unique identifier, a user friendly display
name, and a longer form description.

fromentity_subscription.modelsimportMediumMedium.objects.create(name='in_site',display_name='In Site',description='Notifications available in the Accounts/Notifications tab.')

Source and Medium Considerations

Both Source and Medium objects can be effectively used as
static records that are setup as initial data for an application, or
as dynamic records that change as the various sources and mediums for
notification change. It is important to consider, however, that
excessively dynamic sources and mediums will make it difficult for
individual entities to control their subscriptions.

Subscriptions and Unsubscribing

Entities and groups of entities can be subscribed to
notifications. Once subscribed, individuals, mirrored as entities, can
choose to unsubscribe from notifications for a given source and
medium.

Subscriptions

Subscriptions will most often be created by the application, for an
entire group of entities. In this case, all the entities will receive
the notification, unless they later opt out. Subscriptions can also be
created for an individual entity to receive a certain type of
notification, as an opt-in subscription.

This library includes the table Subscription, available from
entity_subscription.models.Subscription. Creating a
Subscription object is straightforward, assuming the relevant
Source and Medium objects have been created (See “Sources and
Mediums” above), and the entities to be subscribed and their group are
appropriately mirrored. From there, we can use the standard
objects.create interface.

Given the sources and mediums created above, and a relationship
between MyUser and MyGroup in a given application, the
following is a subscription for all the users in a particular group:

Each Subscription object stored in the database only subscribes
the group of entities to a single combination of a Source and
Medium. To create subscriptions for delivering notifications from
the same source over different mediums, a new Subscription object
must be created for each source/medium combination. This allows the
application developer and the users to have detailed control over what
the users are notified about, and how those notifications are
delivered.

Unsubscribing

Individual users of your application may wish to remove themselves
from receiving certain types of notifications.

To unsubscribe an individual from from receiving notifications of a
given source/medium combination is as simple as creating an
Unsubscribe object. Assuming that “Robert” was subscribed to New
Product notifications in the subscription object above, unsubscribing
him from these notifications looks like:

With this object created, the rest of the group will receive these
notifications still, however “Robert” will no longer see them.

Subscriptions and Unsubscribing Considerations

Separating subscriptions and unsubscriptions into separate tables
allows for groups of entities to be subscribed with a single object in
the Subscription table. This is useful for subscribing large
groups of users to a notification by default.

If a given notification may only have a few users interested in
receiving, it may make more sense for it to be an opt-in notification,
where a Subscription object is made for each single entity that wishes
to opt in (that is, a Subscription object with a
subentity_kind=None). This may make more sense then subscribing
large groups to this notification and having most of them unsubscribe.

Checking Subscriptions

Once your sites subscriptions are stored as shown above, you will want
to use those subscriptions to decide to deliver (or not deliver)
notifications. The entity_subscription app provides a couple
methods to make it easier to find who is subscribed to what.

The SubscriptionManager

The following methods are available from the manager of the
Subscription model.

mediums_subscribed(source, entity, subentity_kind=None)

Return a queryset of all the mediums the given entity is
subscribed to, for the given source.

If the optional subentity_kind parameter is given, return
every medium that any of the given entity’s sub-entities, of
the given EntityKind, is subscribed to.

is_subscribed(source, medium, entity, subentity_kind=None)

Return a Boolean, indicating if the entity is subscribed to the
given source on the given medium.

If the optional subentity_kind parameter is not None,
return True if any of the entity’s sub-entities, of the
given type, are subscribed to the given source on the given
medium.

In the common case, checking for subscriptions involves looking at the
mediums a single entity is subscribed to. In this case both
mediums_subscribed and is_subscribed should behave exactly as
expected. Their exact behavior is described in more detail below, in
the section “Checking if an individual entity is subscribed”.

The implications of including a subentity_kind argument are
somewhat more subtle. These implications are described in more detail
below, in the section “Checking if anyone in a group is subscribed”.

Checking if an individual entity is subscribed

Before sending notifications to users, your application wants to make
sure that it’s sending those notifications to users who have been
included through a subscription, and not excluded themselves by
unsubscribing.

To check the subscription status of a single entity, simply call
mediums_subscribed if you want a list of all the mediums an entity
is subscribed to, for a given source, or call is_subscribed if you
want to check if that entity is subscribed to a particular medium for
a given source. When checking the subscription status of a single
entity, the subentity_kind argument should be left as None.

When mediums_subscribed or is_subscribed are called without a
subentity_kind argument, the behavior of these methods is
straightforward. They will return a medium, or return true for that
medium, only if:

1. The entity is part of a individual subscription, or is part of a
group subscription for the given source.

The entity is not unsubscribed from that source and medium.

Once you have checked that an individual entity is subscribed to a
given source/medium combination, you can be confident in delivering
that notification.

Checking if anyone in a group is subscribed

In some cases, your application may have an event that applies to a
group of individuals, and you may wish to check if any of those
individuals are subscribed to receive notifications for that
event.

Both mediums_subscribed and is_subscribed can also take an
optional parameter subentity_kind which will change their
behavior fairly significantly. In this case, the provided argument,
entity, is assumed to be a super-entity, and these functions
return values based on what any of the sub entities are subscribed
to.

So, passing in a super-entity, and subentity-type to either
mediums_subscribed or is_subscribed can provide a useful start
for delivering notifications.

Note that this is only an approximation of what individuals in the
group are subscribed to. Before actually delivering a notification
to any subentity, the application must check that each user is
actually subscribed to receive that notification.

Filtering entities based on subscriptions

Given some number of entities, that may or may not be subscribed to
notifications from a given source and medium, it could be complicated
to determine all the possible entity relationships, and the relevant
subscriptions and unsubscriptions to check exactly which of those
entities should be notified. The entity-subscription framework
provides a method, Subscription.objects.filter_not_subscribed that
will take the list of entities and return only those that should
definitely recieve the notification.

This method returns a queryset of entities to be notified. It takes
into account all possible group subscriptions the entities may belong
to, as well as removing entities that are unsubscribed from these
notifications.

It does, require, however, that all the entities provided are of the
same entity_kind.

Release notes

0.4.0

Migrated Django Entity Subscription to use the EntityKind model for specifying

different kinds of entities. This was a new addition in Django Entity 1.5. Schema migrations
are provided that remove the subentity_typeContentType variable from the Subscription
model and add the subentity_kindEntityKind variable. Note that it is up to the
user to write the appropriate data migration for converting entity types to entity kinds.